At present, phenol-, amine-, phosphite- and thioester-based antioxidants are used to prevent oxidative degradation of polymers. These antioxidants may be used alone or in combination, and they have their own limitations. Specifically, although phenol-based antioxidants have good thermal stability initially, their use is limited because they tend to be colored after oxidation. Amine-based antioxidants exhibit excellent performance, but they have inherent colors. And, phosphite-based antioxidants are not only subject to hydrolysis upon contact with water but also to decomposition during vulcanization for rubber synthesis. Thioester-based antioxidants do not fully exert their performance when used alone and need other primary antioxidants.
Although 2,6-di-t-butyl-4-methylphenol (BHT), which is commonly added to polymers has good thermal stability as a primary antioxidant, it is volatile because of its low molecular weight. As a result, the performance of heat-resistant additives decreases and severe discoloration may occur. Particularly, BHT is known to affect the liver and may cause allergies and tumors.
Because of the environmental pollution problem of the volatile BHT, BHT-free polymer products are demanded by industries. Accordingly, there is an urgent need for the development of an antioxidant not harmful to humans and less volatile while being capable of preventing oxidation of polymers and maintaining physical properties thereof.
Although 1076 (octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate), 1010 (pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate]), or the like are used as replacements for BHT, they require the addition of secondary antioxidants since they are limited in performance as primary antioxidants and physical properties.